Zirconia porous body and manufacturing method thereof

ABSTRACT

A zirconia porous body with excellent stability of heat resistance is manufactured. This relates to a zirconia porous body having peaks at pore diameters of 8 to 20 nm and 30 to 100 nm in a pore distribution based on the BJH method, with a total pore volume of 0.4 cc/g or more, and to a zirconia porous body having a peak at a pore diameters of 20 to 110 nm in a pore distribution based on the BJH method, with a total pore volume of 0.4 cc/g or more.

FIELD OF THE INVENTION

The present invention relates to a novel zirconia porous body and to amanufacturing method thereof.

DESCRIPTION OF THE RELATED ART

Conventionally, the specific surface area at 400° C. of zirconia bodiesused as catalyst carriers has been at most about 100 m²/g. Moreover,those with greater specific surface areas are generally amorphous,without a specific structure. Consequently, stable performance at hightemperatures cannot be obtained with a simple zirconia body used as acatalyst carrier because the specific surface area is reduced at hightemperatures of 400° C. or more. As a result, further improvements inheat resistance (thermal stability) need to be made for purposes of useas a catalyst carrier.

In contrast, in general zirconia-ceria compositions consisting ofzirconium oxide and cerium oxide are more useful in terms of thermalstability than zirconia as catalysts capable of maintaining a relativelylarge specific surface area even at a high temperature of 1000° C.

In Japanese Unexamined Patent Publication No. 2001-170500, it isdisclosed that “porous bodies, each being characterized in that thecenter diameter of the pores is in the range of a mesopore region, thedistribution of the pores is sharp, at least a portion of the porescommunicates in three-dimensional reticular form, the communicationpaths are random and have three-dimensional reticular structure andfiber-like structure is not substantially included,” “porous bodieswherein the aforementioned center diameter is in the range of 2 to 100nm,” “porous bodies wherein 70% or more of the meso-pore volume (volumeof pores in the range of 2 to 100 nm) is within ±5 nm of the centerdiameter of the pores in the meso-pore region,” and “zirconia porousbodies which are porous bodies wherein 40% or more of the mesoporevolume (volume of pores in the range of 2 to 100 nm) is within ±5 nm ofthe center diameter of the pores in the mesopore region” aremanufactured by “precipitating at least part of the aluminum componentfrom an aqueous aluminum salt solution in the range of pH 3 to 4.5,maintaining an aqueous solution containing the precipitate for a fixedtime in an atmosphere of saturated steam or approaching saturated steamto produce a precursor and then baking the precursor.”

Moreover, Japanese Patent No. 3129097 discloses that “porous tetragonalzirconium oxide particles for liquid chromatography having a averageparticle size of 0.5 to 300 microns and a average pore diameter of 20 to300 angstroms (2 to 30 nm) and containing 0.1 to 10% silica by weight”are manufactured by “first heating a zirconium oxide sol produced byadding a zirconium salt and a silicon compound to an alkaline aqueoussolution for 8 or more hours at 80 to 150° C. in an alkaline aqueoussolution, and then forming grains which are baked at 200 to 1000° C.,”and how the aforementioned tetragonal zirconium oxide particles “have apore volume of 0.17 to 0.42 ml/g.”

In Japanese Patent No. 3016865, it is disclosed that “a mixed cerium orzirconium oxide having a total pore volume of at least 0.6 cm³/g whereinat least 50% of the total pore capacity consists of pores having adiameter of 10 to 100 nm” is manufactured by “in a method formanufacturing a mixed cerium or zirconium oxide, preparing a liquidmixture containing a trivalent cerium or zirconium compound; bringingthis mixture into contact with (i) a carbonate or bicarbonate and (ii) abase so that the pH of the reactive medium remains neutral or basicbetween the reactions; collecting a precipitate containing a ceriumcarbonate compound; and baking that precipitate,” and how that oxide“has a specific surface area of at least 20 m²/g after being baked for 6hours at 800° C.”

However, although the specific surface area and total pore volume arenot described in Japanese Unexamined Patent Publication No. 2001-170500,it would seem from the fact that the central pore diameter of 9.5 nmwhen baked at 400° C. increases to 20.5 nm upon baking at 600° C. thatthermal stability at high temperatures (about 1000° C.) isunsatisfactory.

In Japanese Patent No. 3129097, the pore volume of 0.17 to 0.42 ml/g issmall. In this case it would be difficult to obtain adequate propertiesfor various uses such as catalysts.

In Japanese Patent No. 3016865, the specific surface area upon bakingfor 6 hours at 900° C. is at most 35 m²/g, so further improvement isnecessary from the standpoint of thermal stability.

SUMMARY OF THE INVENTION

Consequently, it is a principle object of the present invention toprovide a zirconia porous body with excellent thermal stability.

The inventors perfected the present invention when they discovered as aresult of research in light of the problems of related art that theaforementioned object could be achieved by means of a porous bodyobtained by adoption of specific steps.

That is, the present invention relates to the following zirconia porousbody and manufacturing method therefor.

1. A zirconia porous body having peaks at pore diameters of 8 to 20 nmand 30 to 100 nm in a pore distribution based on the BJH method, with atotal pore capacity of 0.4 cc/g or more.

2. A zirconia porous body according to 1 above, wherein the total volumeof pores having a diameter of 20 to 200 nm is 50% or more of the totalpore volume.

3. A zirconia porous body having a peak at a pore diameters of 20 to 110nm in a pore distribution based on the BJH method, wherein the totalpore volume is 0.4 cc/g or more.

4. A zirconia porous body according to 3 above, wherein the total volumeof pores having a diameter of 10 to 100 nm is 50% or more of the totalpore volume.

5. A zirconia porous body according to any of 1 through 4 above, whereinthe primary particle size is 5 to 30 nm.

6. A zirconia porous body according to any of 1 through 5 above, whereinthe specific surface area after 3 hours of baking at 1000° C. is atleast 30 m²/g.

7. A method for manufacturing a zirconia porous body, which is a methodfor manufacturing a zirconia porous body having:

-   -   (1) a first step wherein basic zirconium sulfate-containing        reaction liquid A, which is prepared by mixing a sulfating agent        at a temperature of at least 80° C. but less than 95° C. with a        zirconium salt solution at a temperature of at least 80° C. but        less than 95° C., is mixed with basic zirconium        sulfate-containing reaction liquid B, which is prepared by        mixing a sulfating agent at a temperature of at least 65° C. but        less than 80° C. with a zirconium salt solution at a temperature        of at least 65° C. but less than 80° C.,    -   (2) a second step wherein the reaction liquid obtained in the        first step is aged at a temperature of 95° C. or more,    -   (3) a third step wherein zirconium hydroxide is produced by        adding alkali to the mixture obtained in the second step to        neutralize the aforementioned basic zirconium sulfate, and    -   (4) a fourth step wherein the aforementioned zirconium hydroxide        is heat treated to obtain a zirconia porous body.

8. A manufacturing method according to 7 above, wherein in thepreparation of the aforementioned reaction liquid A and/or reactionliquid B the sulfating agent and zirconium salt solution are mixed sothat the production speed with basic zirconium sulfate converted tozirconium oxide is 20 g/min/L or less.

9. A manufacturing method according to 8 above, wherein the proportionof the aforementioned reaction liquid A mixed with the aforementionedreaction liquid B is at least 0.1 but less than 1 as a liquid volumeratio of reaction liquid A/(reaction liquid A+reaction liquid B).

10. A method for manufacturing a zirconia porous body, which is a methodfor manufacturing a zirconia porous body having:

-   -   (1) a first step wherein a basic zirconium sulfate-containing        reaction liquid A is prepared by mixing a sulfating agent at a        temperature of at least 80° C. but less than 95° C. with a        zirconium salt solution at a temperature of at least 80° C. but        less than 95° C. so that the production speed with basic        zirconium sulfate converted to zirconium oxide is 20 g/min/L or        less,    -   (2) a second step wherein the reaction liquid obtained in the        first step is aged at 95° C. or more,    -   (3) a third step wherein zirconium hydroxide is produced by        adding alkali to the mixture obtained in the second step to        neutralize the aforementioned basic zirconium sulfate, and    -   (4) a fourth step wherein the aforementioned zirconium hydroxide        is heat treated to obtain a zirconia porous body.

11. A manufacturing method according to any of 7 through 10 above,wherein the free acid concentration of the aforementioned reactionliquid A is 0.1 to 2.0 N.

12. A manufacturing method according to any of 7 through 9 above,wherein the free acid concentration of the aforementioned reactionliquid B is 0.1 to 2.0 N.

13. A manufacturing method according to any of 7 through 12 above,comprising a step of adding a compound of at least one of the rare earthelements, transitional metal elements, Ca, Mg, Al, Si and Zn during atleast one of the first through fourth steps.

14. A manufacturing method according to any of 7 through 12 above,comprising a step of adding a salt of at least one of the rare earthelements, transitional metal elements, Ca, Mg, Al, Si and Zn to thebasic zirconium sulfate.

15. A manufacturing method according to any of 7 through 12 above,comprising a step of adding an oxide and/or hydroxide of at least one ofthe rare earth elements, transitional metal elements, Ca, Mg, Al, Si andZn to the zirconium hydroxide.

ADVANTAGES OF THE INVENTION

In a known method, basic zirconium sulfate was produced by “mixing asulfating agent at room temperature and a zirconium salt solution atroom temperature, raising the temperature to between 65° C. and lessthan 80° C. and maintaining it for a fixed time (aging)” to producebasic zirconium sulfate which was then neutralized with alkali and theresulting hydroxide baked to manufacture a zirconia porous body.

However, the main properties of the zirconia porous body which is thefinal product are a) mainly determined at the stage of producing thebasic zirconium sulfate and b) difficult to control in the case ofwell-known co-precipitation with alkali. Consequently, as shown in FIG.1 under “Conventional Method,” in terms of the relationship between porediameter and pore volume exhibits a sharp distribution with a peak atabout 7 to 10 nm, while the total pore volume is about 0.2 to 0.4 cc/g.This makes it liable to sintering when baked at high temperatures, sothat for example while the specific surface area is 80 to 150 m²/g uponbaking at 400° C. it falls to less than 30 m²/g upon baking at 1000° C.This does not necessarily fulfill the demands for thermal stability of acatalyst material to be used for waste gas treatment in internalcombustion engines.

In contrast, the zirconia porous body of the present invention canprovide excellent effects in terms of thermal stability because it has aspecific pore structure. That is, even when it is heated at hightemperatures the decrease in specific surface area can be effectivelycontrolled. As a result, it can retain a higher specific surface areathan conventional products.

The zirconia porous body having characteristics according to the presentinvention is useful as a catalyst carrier. It can be preferably used asa catalyst material to be used for waste gas treatment in internalcombustion engines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the pore distributions of porous bodiesobtained in Example 1 and Example 2 and by a conventional method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Zirconia Porous Body

The zirconia porous body of the present invention features a specificpore structure. More specifically, it features the following firstporous body and second porous body (both of which are generally called“the porous body of the present invention”).

The first porous body has peaks at pore diameters of 8 to 20 nm and 30to 100 nm in a pore distribution based on the BJH method, with a totalpore volume of 0.4 cc/g or more. The aforementioned pore distribution ismeasured by the equipment and methods shown in Example 1 below, and isexpressed with “pore volume” on the vertical axis and “pore diameter” onthe horizontal axis as shown in FIG. 1. Superior thermal stability canbe achieved by adopting this pore structure. From this standpoint, it isparticularly desirable that the aforementioned peaks appear at 10 to 18nm and 40 to 70 nm.

Moreover, although the aforementioned total pore volume is usually 0.4cc/g or more, it is particularly desirable that it be 0.5 cc/g or more.The upper limit of total pore volume is not specified but is normallyabout 0.7 to 0.9 cc/g.

It is desirable in the first porous body that the total volume of poreshaving a diameter of 20 to 200 nm (particularly 30 to 180 mm) be 50% ormore of the total pore volume.

The second porous body has a peak at a pore diameter of 20 to 110 nm ina pore distribution obtained by the BJH method, with a total pore volumeof 0.4 cc/g or more. Superior thermal stability can be obtained byadopting this pore structure. From this standpoint, it is particularlydesirable that the aforementioned peak be at 25 to 90 nm or preferably30 to 70 nm.

Moreover, although the aforementioned total pore volume is normally 0.4cc/g or more, it is particularly desirable that it be 0.5 cc/g or more.The upper limit of total pore volume is not specified but is normallyabout 0.7 to 0.9 cc/g.

It is desirable in the second porous body that the total volume of poreshaving a diameter of 10 to 100 nm (particularly 25 to 90 mm) be 50% ormore of the total pore volume.

The porous body of the present invention has a structure in which theprimary particles normally connect three-dimensionally. The primaryparticle size (averege particle size) as calculated by X-ray analysis isnot particularly limited in this case but is normally 5 to 30 nm. Betterthermal stability can be obtained because the porous body is composed ofprimary particles having this particle size.

In the porous body of the present invention the specific surface area(BET method) after 3 hours of baking at 1000° C. is preferably 30 m²/gor more while the specific surface area after 3 hours baking at 1050° C.is preferably 25 m²/g or more. The porous body of the present inventionis thermally very stable, with the decrease in specific surface areaeffectively controlled even with a heat history. As a result, it canmaintain a higher specific surface area than conventional products underhigh temperature conditions. The aforementioned specific surface areameans a specific surface area of a zirconia porous body obtained bybaking a porous body at 1000° C. for 3 hours. The porous body isobtained by heating zirconium hydroxide at 400° C. as in Example 1 belowfor example.

The porous body of the present invention is substantially composed ofzirconium oxide (ZrO₂), but when a third component have been added asdescribed below the component may also be included. When the thirdcomponent is included it becomes a solid solution or mixed oxidecomprising these. There are no particular limits on the percentagecontent of the third component(s), which can normally be less than 50%by weight or particularly 1 to 49% by weight of the porous body of thepresent invention. Unavoidable impurities may also be contained to theextent that they do not interfere with the profitable effects of thepresent invention.

2. Method for Manufacturing Zirconia Porous Body

There are no limits on the method for manufacturing the porous body ofthe present invention as long as a porous body is obtained having astructure as described above, but in particular it can be favorablymanufactured by the manufacturing method of the present invention. Thatis, it is preferably manufactured by the first method and second methodshown below.

The manufacturing method for a zirconia porous body of the first methodcomprises:

-   (1) a first step of mixing basic zirconium sulfate-containing    reaction liquid A, which is prepared by mixing a sulfating agent at    a temperature of at least 80° C. but less than 95° C. with a    zirconium salt solution at a temperature of at least 80° C. but less    than 95° C., with basic zirconium sulfate-containing reaction liquid    B, which is prepared by mixing a sulfating agent at a temperature of    at least 65° C. but less than 80° C. with a zirconium salt solution    at a temperature of at least 65° C. but less than 80° C.,    -   (2) a second step of aging the reaction liquid obtained in the        first step at a temperature of 95° C. or more,    -   (3) a third step of producing zirconium hydroxide by adding        alkali to the mixture obtained in the second step to neutralize        the basic zirconium sulfate, and    -   (4) a fourth step of heat-treating the zirconium hydroxide to        obtain a zirconia porous body.

The manufacturing method of a zirconia porous body of the second methodcomprises:

-   -   (1) a first step of preparing a basic zirconium        sulfate-containing reaction liquid A by mixing a sulfating agent        at a temperature of at least 80° C. but less than 95° C. with a        zirconium salt solution at a temperature of at least 80° C. but        less than 95° C. so that the production speed with basic        zirconium sulfate converted to zirconium oxide is 20 g/min/L or        less,    -   (2) a second step of aging the reaction liquid obtained in the        first step at 95° C. or more,    -   (3) a third step of producing zirconium hydroxide by adding        alkali to the mixture obtained in the second step to neutralize        the basic zirconium sulfate, and    -   (4) a fourth step of heat-treating the zirconium hydroxide to        obtain a zirconia porous body.

The various steps for the first method and second method are explainedbelow. Since the second through fourth steps are the same for bothmethods, they are explained together.

First Step (First Method)

In the first step of the first method, basic zirconiumsulfate-containing reaction liquid A, which is prepared by mixing asulfating agent at a temperature of at least 80° C. but less than 95° C.with a zirconium salt solution at a temperature of at least 80° C. butless than 95° C., is mixed with basic zirconium sulfate-containingreaction liquid B, which is prepared by mixing a sulfating agent at atemperature of at least 65° C. but less than 80° C. with a zirconiumsalt solution at a temperature of at least 65° C. but less than 80° C.

The sulfating agent used in reaction liquids A and B may be any whichreacts with zirconium ions to produce a sulfate (that is, to sulfate)and examples include sodium sulfate, ammonium sulfate and the like. Thesulfating agent may be in any form such as a powder, solution or thelike. Of these, a solution (particularly an aqueous solution) is used bypreference. When using it as a solution, the concentration can be set asappropriate.

A solution obtained by dissolving a zirconium salt in a solvent can beused as the zirconium salt solution used in reaction liquids A and B.The zirconium salt is not limited as long as it is one which supplieszirconium ions, and for example one or two or more of zirconiumoxynitrate, zirconium oxychloride, zirconium nitrate and the like can beused. Of these, zirconium oxychloride is used by preference from thestandpoint of superior productivity on an industrial scale. Theaforementioned solvent may be selected appropriately according to thetype of zirconium salt used and the like, but normally water is used bypreference.

There are no particular limits on the concentration of the zirconiumsalt solution, which should normally be 5 to 200 g or particularly 50 to100 g of zirconium oxide (ZrO₂) per 1000 g of solvent.

A basic zirconium sulfate-containing reaction liquid is prepared bymixing the sulfating agent with the zirconium salt solution. In thiscase, a sulfating agent and zirconium salt solution at a temperature ofat least 80° C. but less than 95° C. are mixed in the case of reactionliquid A. In the case of reaction liquid B, a sulfating agent andzirconium salt solution are mixed at a temperature of at least 65° C.but less than 80° C. That is, the sulfating agent and zirconium saltsolution are heated ahead of time to the aforementioned temperature, andthe sulfating agent and zirconium salt solution are mixed whilemaintaining that temperature. In this way, by using a reaction liquidwhich is mixed at the aforementioned temperature, it is possible tocontrol the properties (for example, pore diameter peak locations, totalpore volume, heat resistance of specific surface area, cohesion ofprimary particles and the like) of the zirconia porous body which is thefinal product to the desired values.

Mixing of the sulfating agent and zirconium salt solution can beaccomplished so that a basic zirconium sulfate is produced by thereaction of the two. The sulfating agent and zirconium salt are reactedat a temperature of 65° C. or more to produce a basic zirconium sulfate.

In preparing reaction liquid A and/or reaction liquid B (particularlyreaction liquid A), the sulfating agent and zirconium salt solution canbe mixed so that the production speed with basic zirconium sulfateconverted to zirconium oxide is 20 g/min/L or less (particularly 15g/min/L or less or preferably 10 g/min/L or less). In this way, theaforementioned properties of the resulting zirconia porous body can becontrolled. It is particularly effective that the proportion of thereaction liquid A mixed with said reaction liquid B be at least 0.1 butless than 1 (preferably 0.1 to 0.9, more preferably 0.2 to 0.8) as aliquid volume ratio of reaction liquid A/(reaction liquid A+reactionliquid B). There are no limits on the methods of controlling thereaction speed within the aforementioned range, and for example a methodof dripping one reaction liquid into the other reaction liquid at aspecific speed or the like can be employed.

In the present invention, “with basic zirconium sulfate converted tozirconium oxide” signifies that basic zirconium sulfate is expressed bythe general formula {ZrO (OH)₂}_(x)·(ZrOSO₄)_(1−x) (0<x<1), converted tozirconium oxide in anticipation of the zirconium in the basic zirconiumsulfate becoming zirconium oxide as the final product, since molecularweight cannot be determined unequivocally.

The production speed in the present invention is the speed with 16%zirconium oxychloride added to a 25% sodium sulfate solution.

Moreover, the aforementioned “production speed” in the present inventionis the production speed per 1 L liquid volume after completion ofmixing. That is, the production speed signifies the value obtained bydividing the total production volume by the time (in minutes) frominitiation till completion of mixing, and dividing the result by theliquid volume (L) after completion of mixing.

Moreover, in the present invention reaction liquid A and/or reactionliquid B can be used as two or more reaction liquids with differenttemperatures within the aforementioned temperature range. For example,when reaction liquid A consists of two liquids, a reaction liquid A-1obtained by mixing a sulfating agent at a temperature of at least 80° C.but less than 85° C. with a zirconium salt solution at a temperature ofat least 80° C. but less than 85° C. and a reaction liquid A-2 obtainedby mixing a sulfating agent at a temperature of at least 85° C. but lessthan 95° C. with a zirconium salt solution at a temperature of at least85° C. but less than 95° C. can be used as reaction liquid A. Moreover,for example when reaction liquid B consists of two liquids, a reactionliquid B-1 obtained by mixing a sulfating agent at a temperature of atleast 65° C. but less than 70° C. with a zirconium salt solution at atemperature of at least 65° C. but less than 70° C. and a reactionliquid B-2 obtained by mixing a sulfating agent at a temperature of atleast 70° C. but less than 80° C. with a zirconium salt solution at atemperature of at least 70° C. but less than 80° C. can be used asreaction liquid B. By thus using liquids at different temperatures it ispossible to more precisely control the pore structure of the zirconiaporous body.

In the present invention, the free acid concentration of reaction liquidA and/or B is preferably 0.1 to 2.0 N. Setting the free acidconcentration within the aforementioned range allows the agglomeratewhich makes up the porous body of the present invention to be moreaccurately controlled. The free acid concentration can be adjusted usinghydrochloric acid, sulfuric acid or the like for example. In the presentinvention it is particularly desirable to use hydrochloric acid.

Next, reaction liquid A is mixed with reaction liquid B. There are noparticular limits on the mixing method, mixing order and the like. Themixed proportions of the two can be determined appropriately accordingto the use, desired properties and the like of the porous body withinthe range of generally reaction liquid A:reaction liquid B=1:0.1−9 inzirconium oxide conversion.

First Step (Second Method)

In the first step of the second method, basic zirconiumsulfate-containing reaction liquid A is prepared by mixing a sulfatingagent at a temperature of at least 80° C. but less than 95° C. with azirconium salt solution at a temperature of at least 80° C. but lessthan 95° C. so that the production speed with basic zirconium sulfateconverted to zirconium oxide is 20 g/min/L or less.

The sulfating agent and zirconium salt solution can be the same as thoseused in the first step of the first method above.

In mixing the sulfating agent and zirconium salt solution the productionspeed with basic zirconium sulfate converted to zirconium oxide isnormally 20 g/min/L or less, but 15 g/min/L or less is preferable and 10g/min/L or less is more preferable.

Second Step (First and Second Methods)

In the second step, the reaction liquid obtained in the first step isaged at 95° C. or more (without being cooled first). Through the secondstep it is possible to ensure a high yield by means of completeproduction of basic zirconium sulfate. The upper limit of the agingtemperature can be set so that the reaction liquid does not boil. Theaging time can be set appropriately according to the aforementionedtemperature and the like, but is normally 0.5 hours or more orespecially 1 hour or more.

Third Step (First and Second Methods)

In the third step, alkali is added to the reaction liquid obtained inthe second step to neutralize the aforementioned basic zirconiumsulfate, producing zirconium hydroxide.

There are no particular limits on the alkali, and for example ammoniumhydroxide, ammonium bicarbonate, sodium hydroxide, potassium hydroxideand the like can be used. The amount of alkali added can be any capableof producing a precipitate from the aforementioned reaction liquid, andthe pH of the reaction liquid should normally be 9 or more or preferably10 or more. The alkali can be added in its original form or in the formof a solution obtained by dissolving it in an appropriate solvent (suchas water).

The resulting precipitate may be collected by a known solid-liquidseparation method such as filtration, centrifugation, decantation or thelike. After collection, it can be water washed as necessary. A dryingprocess can also be applied as necessary. The drying process can beeither natural drying, heat drying or the like. Moreover, apulverization process, classification process or the like can also beapplied after drying.

Fourth Step (First and Second Methods)

In the fourth step, the zirconium hydroxide is heat-treated to obtain azirconia porous body.

The heat treatment temperature can normally be in the range of 400 to1100° C. The heat treatment time can be set appropriately according tothe heat treatment temperature and the like, but normally about 1 to 5hours is desirable. There are no particular limits on the heat treatmentatmosphere, but atmospheric air (ambient air) or an oxidizing atmosphereis used.

In the manufacturing method of the present invention, a compound(generally called a “third component”) of at least one of the rare earthelements, transitional metal elements, Ca, Mg, Al, Si and Zn (preferablya rare earth element) can be added during at least one of the firstthrough fourth steps. In this way it is possible to impart the desiredmaterial properties to the resulting zirconia porous body.

Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd and otherlanthanoid elements for example. Examples of transitional metal elementsinclude Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, W and the like. The thirdcomponent compound can be in any form such as a metal salt (nitrate,sulfate, chloride, carbonate or other inorganic acid salt or oxalate,acetate or other organic acid salt) or a hydroxide, oxide or the like.These can be determined appropriately according to the stage of additionand the like. For example, when addition is to the basic zirconiumsulfate it is desirable to add at least one salt of a rare earthelement, transitional metal element, Ca, Mg, Al, Si or Zn. When additionis to the zirconium hydroxide, it is desirable to add at least one oxideand/or hydroxide of a rare earth element, transitional metal salt, Ca,Mg, Al, Si and Zn. When using an oxide and/or hydroxide, it is desirableto apply a pre-treatment such as baking at 1100° C. or more for exampleso as not to adversely affect the properties of the target zirconiaporous body.

The third component can be added in its original form, but is preferablyadded in the form of an ion of the third component in particular. Theion concentration in this case can be set appropriately according to thetype of third component and the like.

The amount of third component added can be set appropriately accordingto the type of element added, the desired material properties and thelike, but normally less than 50% or specifically 1 to 49% by weight ofthe zirconia porous body is desirable. When a third component is used,the finally obtained zirconia porous body becomes a solid solution orcomposite oxide comprising this components.

EXAMPLES

The features of the present invention are explained in more detail belowusing examples. However, the scope of the present invention is notlimited to the scope of these examples.

The material properties in the examples are measured by the followingmethods. Moreover, the materials obtained in the various examples andcomparative examples each contain 1 to 2% by weight hafnium oxide as anunavoidable impurity.

(1) Specific Surface Area

Measured by the BET method using a surface area analyzer (Flowsorb II,Micromeritics).

(2) Pore Volume and Pore Diameter

Measured by the BJH method using the measurement device “Autosorb-1”(Quantachrome, Model No. AS1KR).

(3) Oxygen Storage Capacity (OSC)

Measured by the oxygen pulse method at 600° C. using the measurementdevice “Multitask TPD” (TPD-1-AT, BEL Japan).

(4) Primary Particle Size

Calculated using the following Scherrer equation from the half-valuewidth of the X-ray analysis peak:D=kλ/(β cos θ)

-   -   where k is the constant 0.9, X is the X-ray wavelength (Å), β is        the analytical line width of the sample minus the analytic line        width (radian) of a standard sample, and θ is the analysis        angle.

Example 1

1) 94 g of a 25% sodium sulfate solution was heated to 65° C., 250 g ofa 16% (by ZrO₂ conversion) zirconium oxychloride solution which had beenpreviously heated to 75° C. was added thereto, hydrochloric acid wasadded to achieve a free acid concentration of 1.5 N and this wasmaintained for 0.5 hours to produce basic zirconium sulfate(low-temperature reaction liquid).

2) 141 g of a 25% sodium sulfate solution was heated to 85° C., 375 g ofa 16% (by ZrO₂ conversion) zirconium oxychloride solution which had beenpreviously heated to 85° C. was added thereto, hydrochloric acid wasadded to achieve a free acid concentration of 1.5 N and this wasmaintained for 0.5 hours to produce basic zirconium sulfate(high-temperature reaction liquid).

3) The aforementioned low-temperature reaction liquid andhigh-temperature reaction liquid were mixed, heated to 95° C. andmaintained for 0.5 hours to age them.

4) Next, the aged solution was cooled to room temperature and 125 g of a20% (CeO₂ conversion) cerium sulfate solution was added to and mixeduniformly.

5) 25% sodium hydroxide was added to the resulting mixed solution,neutralizing it to a pH of 13 or more and producing a hydroxideprecipitate.

6) The resulting hydroxide precipitate was filtered and thoroughly waterwashed.

7) After being water washed the hydroxide was dried for 24 hours at 105°C.

8) The dried hydroxide was baked for 5 hours at 400° C. in anatmospheric air to obtain a zirconium oxide-containing zirconium porousbody.

9) The aforementioned porous body was further baked for 3 hours in anatmospheric air at 900 to 1100° C. to obtain a baked product.

10) The aforementioned baked product was subjected to X-ray analysis andthe specific surface area, pore diameter, oxygen storage capacity(OSC)and the like were measured. The composition of the resulting bakedproduct (weight %) is shown in Table 1, while its material propertyvalues are shown in Tables 2 and 3. The pore distribution of a bakedproduct obtained by baking at 1000° C. in 9) above is shown in FIG. 1(“Present Invention 1”). TABLE 1 Composition ZrO₂ CeO₂ TiO₂ Fe₂O₃ Al₂O₃La₂O₃ Nd₂O₃ Example 1 80 20 Example 2 80 20 Comparative 80 20 Example 1Example 3 70 30 Example 4 70 30 Comparative 70 30 Example 2 Example 5 955 Example 6 95 5 Comp. 95 5 Example 3 Example 7 99 1 Example 8 99 1Comparative 99 1 Example 4 Example 9 72 21 1.7 5.3 Example 10 72 21 1.75.3 Comp. 72 21 1.7 5.3 Example 5

TABLE 2 Material property values Primary Total pore particle Porediameter peaks volume size Peak 1 (nm) Peak 2 (nm) (cc/g) (nm) Example 115 50 0.5 12 Example 2 — 52 0.6 12 Comparative 10 — 0.3 12 Example 1Example 3 14 45 0.6 11 Example 4 — 52 0.7 11 Comparative 9 — 0.4 11Example 2 Example 5 12 40 0.6 11 Example 6 — 43 0.7 11 Comparative 12 —0.5 10 Example 3 Example 7 12 48 0.6 10 Example 8 — 50 0.7 10Comparative 9 — 0.4 11 Example 4 Example 9 12 52 0.5 11 Example 10 — 450.7 11 Comparative 10 — 0.3 11 Example 5

TABLE 3 Material property values Specific surface area (m²/g) OSC 400°C. 900° C. 950° C. 1000° C. 1050° C. 1100° C. (μmol-O₂/g) Example 1 12055 50 30 25 15 140 Example 2 120 55 50 35 25 15 140 Comp. Ex. 1 100 4035 20 12 8 120 Example 9 130 65 65 48 43 20 190 Example 10 130 65 65 5548 22 185 Comp. Ex. 5 125 40 37 25 15 8 160

A distribution clearly different from that of “Conventional Method” isshown in FIG. 1. That is, there are two pore diameter peaks, and thetotal pore volume is shown to be about 0.5 cc/g. This zirconia porousbody has a primary particle size in the range of 5 to 30 nm, thespecific surface area after 3 hours of baking at 1000° C. is at least 30m²/g, and the specific surface area after 3 hours of baking at 1050° C.is at least 25 M²/g, indicating a zirconia porous body with an excellentthermal stability of specific surface area and a large total porevolume.

Example 2

1) 237 g of a 25% sodium sulfate solution was heated to 85° C. and 625 gof a 16% (by ZrO₂ conversion) zirconium oxychloride solution which hadbeen previously heated to 85° C. was added thereto. The addition speedof the aforementioned zirconium oxychloride solution here was adjustedso that the production speed of basic zirconium sulfate as converted tozirconium oxide would be about 12 g/minute/L, or about ⅕ the normalspeed. Next, hydrochloric acid was added to achieved a free acidconcentration of 1.5 N, and this was maintained for 0.5 hours to producebasic zirconium sulfate.

2) The aforementioned reaction liquid was first heated to 95° C. andthen maintained for 0.5 hours to age it.

3) Next, the aged solution was cooled to room temperature and 125 g of a20% (CeO₂ conversion) cerium nitrate solution was added to and mixeduniformly.

4) 25% sodium hydroxide was added to the resulting mixed solution toadjust to pH to 13 or more and produce a hydroxide precipitate.

5) The resulting hydroxide precipitate was filtered and thoroughly waterwashed.

6) After being water washed the hydroxide was dried for 24 hours at 105°C.

7) The dried hydroxide was baked for 5 hours at 400° C. in anatmospheric air to obtain a zirconium oxide-containing zirconium porousbody.

8) The aforementioned porous body was further baked for 3 hours in anatmospheric air at 900 to 1100° C. to obtain a baked product.

9) The aforementioned baked product was subjected to X-ray analysis andthe specific surface area, pore diameter, oxygen storage capacity (OSC)and the like were measured. The composition of the resulting bakedproduct (weight %) is shown in Table 1, while its material propertyvalues are shown in Tables 2 and 3. The pore distribution of a bakedproduct obtained by baking at 1000° C. in 8) above is shown in FIG. 1(“Present Invention 2”).

The porous body of the “Conventional Method” in FIG. 1 has a sharpdistribution of pore diameters, with the result that it is liable tosintering when baked at high temperatures, and the thermal stability ofspecific surface area was not necessarily satisfactory. That is, itseems that because in a zirconia porous body manufactured by the“conventional method” “fine particles are densely packed,” there is alarge area of contact between particles which makes it liable tosintering at high temperatures. In contrast, by reducing the productionspeed with basic zirconium sulfate converted to zirconium oxide to ⅓ orless (preferably ⅕ or less) that of the “conventional method” as inExample 2, a zirconia porous body is obtained with the pore diameterdistribution and pore volume shown under “Present Invention 2” in FIG. 1which has excellent thermal stability.

Comparative Example 1 Coprecipitation

1) 625 g of a 16% (ZrO₂ conversion) zirconium oxychloride solution atroom temperature was added to 237 g of a 25% sodium sulfate solution.After addition of hydrochloric acid to achieve a free acid concentrationof 1.5 N, this was heated to 75° C. and maintained for 1 hour to agewhile producing basic zirconium sulfate.

2) Next, the aged solution was cooled to room temperature and 125 g of a20% (CeO₂ conversion) cerium sulfate solution was added to and mixeduniformly.

3) 25% sodium hydroxide was added to the resulting mixed solution,neutralizing it to a pH of 13 or more and producing a hydroxideprecipitate.

4) The resulting hydroxide precipitate was filtered and thoroughly waterwashed.

5) After being water washed the hydroxide was dried for 24 hours at 105°C.

6) The dried hydroxide was baked for 5 hours at 400° C. in atmosphere toobtain a zirconium oxide-containing zirconium porous body.

7) The aforementioned porous body was further baked for 3 hours in anatmospheric air at 900 to 1100° C. to obtain a baked product.

8) The aforementioned baked product was subjected to X-ray analysis andthe specific surface area, pore diameter, oxygen storage capacity(OSC)and the like were measured. The composition of the resulting bakedproduct (weight %) is shown in Table 1, while its material propertyvalues are shown in Tables 2 and 3. The pore distribution of a bakedproduct obtained by baking at 1000° C. in 7) above is shown in FIG. 1(“Conventional Method”).

Example 3

A baked product was manufactured as in Example 1 except that step 4) inExample 1 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% titanium tetrachloride solution was added soas to achieve a titanium oxide (TiO₂) content of 30% by weight of thefinal product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The results are shown in Table 1. The composition (% byweight) of the resulting baked product is shown in Table 1, and thematerial property values in Tables 2 and 3. The pore distribution of aproduct baked at 1000° C. was measured with roughly the same results asthose shown under “Present Invention 1” in FIG. 1.

Example 4

A baked product was manufactured as in Example 2 except that step 3) inExample 2 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% titanium tetrachloride solution was added soas to achieve a titanium oxide (TiO₂) content of 30% by weight of thefinal product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 2” in FIG. 1.

Comparative Example 2

A baked product was manufactured as in Comparative Example 1 except thatstep 2) in Comparative Example 1 was replaced by the following. The agedsolution was cooled to room temperature, and a 15% titaniumtetrachloride solution was added so as to achieve a titanium oxide(TiO₂) content of 30% by weight of the final product (baked product),and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under“Conventional Method” in FIG. 1.

Example 5

A baked product was manufactured as in Example 1 except that step 4) inExample 1 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% iron chloride (III) solution was added so asto achieve a ferric oxide (Fe₂O₃) content of 5% by weight of the finalproduct (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 1” in FIG. 1.

Example 6

A baked product was manufactured as in Example 2 except that step 3) inExample 2 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% iron chloride (III) solution was added so asto achieve a ferric oxide (Fe₂O₃) content of 5% by weight of the finalproduct (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 2” in FIG. 1.

Comparative Example 3

A baked product was manufactured as in Comparative Example 1 except thatstep 2) in Comparative Example 1 was replaced by the following. The agedsolution was cooled to room temperature, and a 15% iron chloride (III)solution was added so as to achieve a ferric oxide (Fe₂O₃) content of 5%by weight of the final product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under“Conventional Method” in FIG. 1.

Example 7

A baked product was manufactured as in Example 1 except that step 4) inExample 1 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% aluminum chloride solution was added so asto achieve an aluminum oxide (Al₂O₃) content of 1% by weight of thefinal product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 1” in FIG. 1.

Example 8

A baked product was manufactured as in Example 2 except that step 3) inExample 2 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% aluminum chloride solution was added so asto achieve an aluminum oxide (Al₂O₃) content of 1% by weight of thefinal product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 2” in FIG. 1.

Comparative Example 4

A baked product was manufactured as in Comparative Example 1 except thatstep 2) in Comparative Example 1 was replaced by the following. The agedsolution was cooled to room temperature, and a 15% aluminum chloridesolution was added so as to achieve an aluminum oxide (Al₂O₃) content of1% by weight of the final product (baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under“Conventional Method” in FIG. 1.

Example 9

A baked product was manufactured as in Example 1 except that step 4) inExample 1 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% cerium nitrate solution was added so as toachieve a cerium oxide (CeO₂) content of 20% of the final product (bakedproduct), together with a 15% lanthanum nitrate solution added so as toachieve a lanthanum oxide (La₂O₃) content of 1.7% of the final product(baked product) and a 15% neodymium nitrate solution added so as toachieve a neodymium oxide (Nd₂O₃) content of 5.3% of the final product(baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 1” in FIG. 1.

Example 10

A baked product was manufactured as in Example 2 except that step 3) inExample 2 was replaced by the following. The aged solution was cooled toroom temperature, and a 15% cerium nitrate solution was added so as toachieve a cerium oxide (CeO₂) content of 20% of the final product (bakedproduct), together with a 15% lanthanum nitrate solution added so as toachieve a lanthanum oxide (La₂O₃) content of 1.7% of the final product(baked product) and a 15% neodymium nitrate solution added so as toachieve a neodymium oxide (Nd₂O₃) content of 5.3% of the final product(baked product), and mixed uniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under “PresentInvention 2” in FIG. 1.

Comparative Example 5

A baked product was manufactured as in Comparative Example 1 except thatstep 2) in Comparative Example 1 was replaced by the following. The agedsolution was cooled to room temperature, and a 15% cerium nitratesolution was added so as to achieve a cerium oxide (CeO₂) content of 20%of the final product (baked product), together with a 15% lanthanumnitrate solution added so as to achieve a lanthanum oxide (La₂O₃)content of 1.7% of the final product (baked product) and a 15% neodymiumnitrate solution added so as to achieve a neodymium oxide (Nd₂O₃)content of 5.3% of the final product (baked product), and mixeduniformly.

The material properties of the resulting baked product were measured asin Example 1. The composition (% by weight) of the resulting bakedproduct is shown in Table 1, and the material property values in Tables2 and 3. The pore distribution of a product baked at 1000° C. wasmeasured with roughly the same results as those shown under“Conventional Method” in FIG. 1.

1. A zirconia porous body having (1) peaks at pore diameters of 8 to 20nm and 30 to 100 nm in a pore distribution based on the BJH method and(2) a total pore volume of 0.4 cc/g or more.
 2. The zirconia porous bodyaccording to claim 1, wherein the volume of pores having a diameter of20 to 200 nm is 50% or more of the total pore volume.
 3. A zirconiaporous body having (1) a peak at a pore diameters of 20 to 110 nm in apore distribution based on the BJH method and (2) a total pore volume is0.4 cc/g or more.
 4. The zirconia porous body according to claim 3,wherein the volume of pores having a diameter of 10 to 100 nm is 50% ormore of the total pore volume.
 5. The zirconia porous body according toclaim 1 or 3, wherein the primary particle size of the particlescontained in the porous body is 5 to 30 nm.
 6. The zirconia porous bodyaccording to any of claims 1 or 3, wherein the specific surface areaafter 3 hours of baking at 1000° C. is at least 30 m²/g.
 7. A method formanufacturing a zirconia porous body, the method comprising: (1) a firststep of mixing basic zirconium sulfate-containing reaction liquid A,which is prepared by mixing a sulfating agent at a temperature of atleast 80° C. but less than 95° C. with a zirconium salt solution at atemperature of at least 80° C. but less than 95° C., with basiczirconium sulfate-containing reaction liquid B, which is prepared bymixing a sulfating agent at a temperature of at least 65° C. but lessthan 80° C. with a zirconium salt solution at a temperature of at least65° C. but less than 80° C., (2) a second step of aging the reactionliquid obtained in the first step at a temperature of 95° C. or more,(3) a third step of producing zirconium hydroxide by adding alkali tothe mixture obtained in the second step to neutralize the basiczirconium sulfate, and (4) a fourth step of heat-treating the zirconiumhydroxide to obtain a zirconia porous body.
 8. The manufacturing methodaccording to claim 7, wherein, in the preparation of the reaction liquidA and/or the reaction liquid B, the sulfating agent and the zirconiumsalt solution are mixed so that the production speed with basiczirconium sulfate converted to zirconium oxide is 20 g/min/L or less. 9.The manufacturing method according to claim 8, wherein the proportion ofthe reaction liquid A mixed with the reaction liquid B is at least 0.1but less than 1 as a liquid volume ratio of reaction liquid A/(reactionliquid A+reaction liquid B).
 10. A method for manufacturing a zirconiaporous body, the method comprising: (1) a first step of preparing abasic zirconium sulfate-containing reaction liquid A by mixing asulfating agent at a temperature of at least 80° C. but less than 95° C.with a zirconium salt solution at a temperature of at least 80° C. butless than 95° C. so that the production speed with basic zirconiumsulfate converted to zirconium oxide is 20 g/min/L or less, (2) a secondstep of aging the reaction liquid obtained in the first step at 95° C.or more, (3) a third step of producing zirconium hydroxide by addingalkali to the mixture obtained in the second step to neutralize thebasic zirconium sulfate, and (4) a fourth step of heat-treating thezirconium hydroxide to obtain a zirconia porous body.
 11. Themanufacturing method according to any of claim 7 or 10, wherein the freeacid concentration of the reaction liquid A is 0.1 to 2.0 N.
 12. Themanufacturing method according to any of claim 7, wherein the free acidconcentration of the reaction liquid B is 0.1 to 2.0 N.
 13. Themanufacturing method according to any of claim 7 or 10, comprising astep of adding a compound of at least one of the rare earth elements,transitional metal elements, Ca, Mg, Al, Si and Zn during at least oneof the first through fourth steps.
 14. The manufacturing methodaccording to any of claim 7 or 10, comprising a step of adding a salt ofat least one of the rare earth elements, transitional metal elements,Ca, Mg, Al, Si and Zn to the basic zirconium sulfate.
 15. Themanufacturing method according to any of claim 7 or 10, comprising astep of adding an oxide and/or hydroxide of at least one of the rareearth elements, transitional metal elements, Ca, Mg, Al, Si and Zn tothe zirconium hydroxide.